Originally Posted by
Bart
Not to get picky, but I don't agree with the term "false positive." In my hand lotion example, the machine did successfully detect the glycerin component in the lotion. That doesn't mean that the bottle contains explosives. It only means that the bottle contains glycerin.
As for "false negative," that tells me that the officer didn't obtain a good sampling.
It's not the machine, it's the machine operator that determines whether or not the item may actually be a threat.
Then the machine is a glycerine detector, and it isn't a reliable explosives detector, which cause a couple problems. 1) it is a false alarm for explosives which causes extra work and 2) the follow up action is corrupted, and the detection system is reduced to the efficacy of the followup procedure.
If, when the machine raises its alarm, the practice is for a screener give a pass on bottles with "glycerine" in the fine print, then you've introduced a hole. If the smuggler in the OP used a case of glycerine-based body wash, everyone would have had a big grin and the detection system would have failed.
(My WAG at what happened is that some of the bottles in the case looked more dense on the x-ray than others: "Some were unusually heavy and many contained a very dark liquid ..." If you looked at an x-ray of a case of beer and 5 of the bottles looked 'oranger' or 'whiter' than the others, you'd tend to notice.)